decompile proguarded apk

i have an apk file which is fully proguarded and really hard to decompile it.. but i need a specific code from this app .. this app sends some data to server and in one of form it sends a value with name RetailerAuthToken which is like some sha 256 hash value maybe sommething else.. so i need someone to figure out for me that how this apk is generatic this RetailerAuthToken.. if you can succesfully find it i can pay for your time... please send your contact details